810 SYSTEMATIC PALEONTOLOGY 



4 cm., averaging about 3 cm. Margins entire, slightly irregular. Texture 

 coriaceous. A wide false midrib in the basal part of some of the leaves is 

 formed by the convergence of the digitate veins which are thin and diverge 

 at acute angles in a flabellate manner and pursue a relatively straight 

 upward course, inosculating in the marginal regions. They send off fre- 

 quent pseudo-dichotomous inosculating branches. An ultimate areolation 

 of thin transverse veins forms an open four or five-sided mesh. The epi- 

 dermis is preserved in some instances. The stomata are few and scattered 

 and are confined to one surface and are altogether absent from the broad 

 leaf-bases. 



In its size, outline, and venation this species is scarcely to be distin- 

 guished from the modern Pistia slratiotes Linne, which is certainly a 

 variable and widely distributed, chiefly tropical, species. In this country 

 it is found from Florida to Texas. Elsewhere it occurs in the West Indies 

 and southward through Mexico and Central America to Paraguay and 

 Argentina. In Africa it is found from Natal to Senegambia and Nubia, 

 occurring also in Madagascar and the Mascarene Islands. In Asia it 

 occurs throughout the East Indies and northward to the Philippines. 



The fossil forms are more like the younger leaves of the modern plant 

 (possibly a phylogenetic character in the latter), the later leaves tending 

 toward a cuneate outline with a truncated apex and straighter sides. 



But few fossils have been referred to this genus. Hosius and von der 

 Marck described in 1880 what they called Pistites loriformis from the 

 Lower Senonian of Westphalia (Pal., Bd. xxvi, p. 182, pi. xxxviii, figs. 

 151, 152), but this is probably cycadean, as Schenk suggested (in 

 Zittel's Handbuch, p. 378, 1890). Lesquereux in 1876 (Ann. Kept. U. S. 

 Geol. and Geog. Survey, Terr., p. 299, 1874) named a remarkably well- 

 preserved form from Point of Eocks, Wyoming, Pistia corrugata. This 

 was fully described and illustrated in his Tertiary Flora (p. 103, pi. Ixi, 

 figs. 1, 3-7, 9-11, 1883) and included leaves of various sizes, and rootlets. 

 It comes from beds belonging to the Montana formation (Senonian) , which 

 are of about the same age as the French beds from which the only other 

 Cretaceous species is known. This latter, Pistia mazelii, was mentioned 



